After 1915, and as a result of the Great War, more than 200 bacterial action compounds were studied, among them hypochlorous acid. Hypochlorous acid was initially detected as an oxidizing agent generated by neutrophils. It was obtained from seawater.
Studies by Dakin in 1917 are reported using sodium hypochlorite diluted to 0.50% as an irrigation liquid for the cleaning and disinfection of contaminated wounds.
Later, in 1958, Agnes investigated hypochlorous acid as an immunological substance and defense mechanisms for granulocytes.
In 1989 Stephan J. Weiss in the New England Journal of Medicine conducted bacterial sensitivity studies on E. coli and toxicity on tissue in guinea-pigs.
There are currently several patents related to the production of hypochlorous acid, as mentioned below:
U.S. Pat. No. 4,190,638 entitled “Production of hypochlorous acid”, owned by PPG Industries Inc., of Feb. 26, 1980 discloses that aqueous acid is produced by precipitating the acid through carbonation in a electrolytic cell where the cathode is liquid which is placed in contact with a bed fluidized with a mixture of gaseous chlorine and water vapor where the gas which is formed from the hypochlorous bed is absorbed by the water.
U.S. Pat. No. 4,908,215 entitled “Hypochlorite compositions containing thiosulphate and their use” of Mar. 13, 1990, discloses a process for disinfection, sterilization, bleaching and cleaning of a liquid or a surface comprised of: (a) producing an aqueous solution of hypochlorite, thiosulphate of earthy alkaline metal and a prebuffer in which the hypochlorite has an initial concentration of about 5 to 5000 ppm of chlorine and a molar ratio of thiosulphate to hypochlorite between 0.25:1 and 0.75:1; (b) adjusting the initial pH of the solution between 9.0 and 11.0 in contact with the surface or the liquid with the solution until the hypochlorite is consumed and the pH of the prebuffer solution decreases while the hypochlorite is consumed by the thiosulphate at the same time as the hypochlorite begins to depend on the initial pH of the solution.
U.S. Pat. No. 5,027,627 entitled “Production of Hypochlorous Acid” published on Aug. 6, 1991, discloses that hypochlorous acid is obtained by reaction of an aqueous solution of an alkaline metal hydroxide, forming drops with the gaseous chlorine to produce hypochlorous acid in vapor and particles of solid alkaline metal; a process where the molar ratio of the gaseous chlorine to the alkaline metal hydroxide is kept at least 22:1. The process includes the formation of impure chlorate in chlorinated alkaline metal particles. The hypochlorous acid produced contains 35-60% of weight dissolved in concentrated chlorine of at least about 2% by weight and is substantially free of ions of the alkaline metal and chlorine.
U.S. Pat. No. 5,322,677 entitled “Process for the production of a concentrated solution of hypochlorous acid”, owned by Oil Corporation, published on Jun. 21, 1994, discloses a process for obtaining an aqueous hypochloric acid solution having an HOCl concentration of 50-60% by weight, which comprises making a aqueous solution of an alkaline metal hydroxide with 50% by weight with excess of chlorine gas react, reacting at 80-120 deg. C. to produce a mixture of monoxide, chlorine, hypochlorous acid vapor and water vapor, solid particles of chlorate alkaline metal of at least 10%.
WO 9514636 entitled “Manufacture of Hypochlorous Acid” owned by Joseph Repman, The Dow Chemical Company Trent and David, L., published Jun. 1, 1995, discloses a process which consists of contacting drops of an aqueous solution of hypochlorite metal having a volume median diameter of 500 mm with chlorine gas to produce hypochlorous acid. At least 80% of the hypochlorous acid produced in the preceding stage is vaporized to provide a vapor phase containing chlorine, water vapor, hypochlorous acid and dichlorine monoxide, leaving a liquid aqueous phase containing hypochlorous acid. The liquid phase hypochlorous acid solution is then distilled using a stripping gas containing at least 20 mole percent chlorine to separate gaseous hypochlorous acid and dichlorine monoxide from the aqueous brine.
U.S. Pat. No. 7,323,118, and the related European patent, EP 1432427, both entitled “Composition of hypochlorous acid and its applications”, Calderon, co-assigned to Aquilabs S. A., disclose a composition of hypochlorous acid with medical applications in humans and in veterinary practice, both prophylactic and therapeutic. The composition of hypochlorous acid has 17 g/l of available chlorine, a pH value of 5-6, a density of 0.9-1.05 g/ml and an oxidation reduction potential of 1250-1450 m.v. The composition of hypochlorous acid is stated to have therapeutic use in a variety of medical applications.
U.S. Pat. No. 7,276,255 entitled “Wound and ulcer treatment with super-oxidized water”, owned by Sterilox Medical (Europe) Limited, discloses a method for treating an open wound comprising administration of a hypochlorous acid solution having a pH value of 4 to 7, a redox potential of >950 mV, and being obtained by electrochemical treatment of a saline solution.
U.S. Pat. No. 6,426,066 entitled “Use of physiologically balanced, ionized, acidic solution in wound healing”, owned by California Pacific Labs, Inc., filed on Jan. 12, 2000, discloses a solution prepared by the electrolysis of a solution comprising a mixture of inorganic salts in physiologically balanced proportions and the use of the physiologically balanced, acidic composition to treat wounds. The disclosed starting solution comprises salts ranging from about 0.4 g/L to about 16 g/L. The electrolyzed solution has a pH value within the range of about 2 to about 6, an oxidation reduction potential within the range of about 600 mV to about 1200 mV and titratable halide content within the range of about 10 ppm to about 100 ppm.
A family of patent applications related to U.S. Pat. No. 6,426,066 [U.S. application Ser. No. 10/000,919, Ser. No. 10/117,667, Ser. No. 10/209,681, Ser. No. 10/655,493 and PCT/US03/19126] disclose variations of the starting solution salt range, pH range, oxidation reduction potential and titratable halide content. The hypochlorous acid solution so prepared is also disclosed to be stable when stored in a chemically non-reactive container at room temperature over at least three months.
Wang et al., “Hypochlorous Acid as a Potential Wound Care Agent: Part I. Stabilized Hypochlorous Acid: A Component of the Inorganic Armamentarium of Innate Immunity”, Journal of Burns and Wounds, 2007, Vol. 6:65-79, and Robson et al., “Hypochlorous Acid as a Potential Wound Care Agent: Part II. Stabilized Hypochlorous Acid: Its Role in Decreasing Tissue Bacterial Bioburden and Overcoming the Inhibition of Infection on Wound Healing”, Journal of Burns and Wounds, 2007, Vol. 6:80-90, disclose the use of a stabilized hypochlorous acid solution prepared by acidifying reagent-grade NaOCl to a pH range of 3.5 to 4.0 with dilute HCl.
None of the above disclosures is believed to teach or suggest an antimicrobial hypochlorous acid solution that has the stability characteristics of those contemplated herein. The disclosure that follows illustrates the preparation of a contemplated stable solution.